1. Field of the Invention
This invention pertains to dial indicators. More particularly, it pertains to such indicators in which two concentric dials cooperate with coaxially driven scale pointers, and in which both dials are angularly adjustable about the pointer axes for presetting, calibration or zeroing of scales on the dials relative to the pointers in any position of the pointers.
2. Review of the Prior Art
Concentric scale dial indicators, in which each dial scale cooperates with a reference member, are known in various applications. Such indicators may be found, for example, in machine tools where concentric rotary dials cooperate with fixed reference members. The dials rotate at different rates as determined by appropriate gearing coupled to a leadscrew in the machine tool. The dials may cooperate with a common stationary reference member or with separate fixed reference members, such as pointers. Usually such indicators have no adjustment capability enabling them to be set to zero or to some specified indication independently of the state of things in the machine tool.
In machine tools, such indicators indicate the distance of travel of one tool part (such as a lathe carriage) along another part (such as a lathe bed) relative to a base or zero position of the carriage on the bed. Typically, one dial indicates such travel in inches and tenths of inches, and a second dial indicates hundredths and thousandths of inches of travel. This proves to be inconvenient and a source of error in many cases. In a complex machining operation, the machinist may desire to move the carriage a desired distance from a first carriage position (not the base position) to a second position (not the base position). To do this correctly, he must ascertain or separately compute the difference between the indicator readings at the two different carriage positions, and then add or subtract that difference to or from the reading for the first position to determine when he has moved the carriage to the second position. Such arithmetic operations are time consuming and mistakes may be made. It would be quicker and more accurate, with the carriage at the first position, to zero or preset the indicator to the known distance of travel, and then move the carriage until it reads either the desired distance or zero, respectively. This cannot be done where the dials are not separately adjustable independently of the leadscrew.
In other applications, concentric dial, rotary pointer indicators are known. In such indicators, two or more concentric circular dials cooperate with corresponding ones of a plurality of coaxially driven rotary pointers. In such indicators, only the outermost dial has been adjustable or prepositionable relative to the pointer.
The present invention currently is provided in the context of a friction wheel measuring device which has significant utility as a measuring accessory for machine tools. U.S. Pat. Nos. 3,311,985 and 3,378,929, for example, owned by the assignee of this invention, pertain to such measuring devices. In the device of U.S. Pat. No. 3,311,985, three dials are provided to give the desired overall indication; only the third and finest reading dial is adjustable; the other two could be preset or zeroed only by disengaging the metering wheel from the surface along which it rolled. In the device of U.S. Pat. No. 3,378,929, the indicators are fully adjustable for zeroing or presetting thereof, but the overall indicator is divided into two separate parts having two spaced axes about which corresponding circular dials are separately adjustable; the metering wheel does not have to be disengaged from its measurement surface. Improvements in these measuring devices have made it possible for them to be made smaller, but at the same time the visual indicators should be as large as possible for ease of reading by the user.
A dual concentric dial indicator, having coaxially driven rotary pointers, is a good indicator for use in the smaller measuring devices because such an indicator can be large relative to the device. However, the problem then becomes one of how to provide full adjustability of the indicator for complete zeroing or presetting of the indicator. It will be apparent, however, that the problem of full adjustability of dual or multiple concentric dial indicators can arise in mechanisms other than friction wheel measuring devices. It is this general problem to which this invention is addressed.